The present invention relates generally to television receivers, and more specifically to display frame rate adaptation in a DC coupled and constant slope ramp vertical deflection system.
FIG. 1 is a system block diagram 100 of an exemplary TV receiver for processing analog or digital format signals. Operation of the receiver 100 will be discussed in the context of National Television Systems Committee (NTSC) and Advanced Television Systems Committee (ATSC) signal standards. However, practice of the inventive aspects laid out herein are not limited to NTSC and ATSC signal standards. Out of the tuner 100, a digital signal DS is fed to a de-multiplexor 102, a known type of digital decoder, which sends a selected video signal to a video decoder 104 that provides red R, green G and blue B color component signals to the picture tube 107. An analog signal AS received from the tuner 101 is fed to an NTSC decoder 104 to provide a selective video signal for further video processing 104, which provides R, G and B color component signals to the picture tube 107. The NTSC signal out of the decoder 103 to the video decoder/processor 104 is format converted from 540P progressive active lines. Horizontal and vertical synchronization signals Hsync and Vsync are generated by a raster generator 105 in response to the video decoding or processing 104. The synchronization signals are then fed to a deflection process 106 that provides vertical and horizontal deflection signals Vert and Horiz to drive deflection coils 108, 109.
Generally, the raster generator 105 must be synchronized to the received signal so that picture frames are displayed at the same rate in which they were transmitted with the video signal. Dropping or repeating of frames is undesirable for the portrayal of motion by quality TV receivers. A reasonable way must be identified for a TV receiver to track the incoming frames to avoid generation of temporal artifacts. There are 18 picture scanning formats and frame rates supported by the ATSC standard, based on frame rates of 60 Hz, 30 Hz and 24 Hz. However, if the NTSC friendly rates of 59.94 Hz, 29.97 Hz and 23.97 Hz are considered, which will permit video reception of NTSC signals during the simulcast period of both ATSC and NTSC, then there are a total of 36 picture formats. Given the number of ATSC picture formats alone, tracking the incoming video picture frame frequency becomes difficult when the objective is a TV deflection system design optimized to work over a narrow range of frequencies.